MainLoop is the abstract base class for a Godot project’s game loop. It is inherited by SceneTree, which is the default game loop implementation used in Godot projects, though it is also possible to write and use one’s own MainLoop subclass instead of the scene tree.

Upon the application start, a MainLoop implementation must be provided to the OS; otherwise, the application will exit. This happens automatically (and a SceneTree is created) unless a main Script is provided from the command line (with e.g. godot-smy_loop.gd, which should then be a MainLoop implementation.

Here is an example script implementing a simple MainLoop:

extendsMainLoopvartime_elapsed=0varkeys_typed=[]varquit=falsefunc_initialize():print("Initialized:")print(" Starting time: %s"%str(time_elapsed))func_idle(delta):time_elapsed+=delta# Return true to end the main loop.returnquitfunc_input_event(event):# Record keys.ifeventisInputEventKeyandevent.pressedand!event.echo:keys_typed.append(OS.get_keycode_string(event.keycode))# Quit on Escape press.ifevent.keycode==KEY_ESCAPE:quit=true# Quit on any mouse click.ifeventisInputEventMouseButton:quit=truefunc_finalize():print("Finalized:")print(" End time: %s"%str(time_elapsed))print(" Keys typed: %s"%var2str(keys_typed))

NOTIFICATION_WM_MOUSE_ENTER = 1002 — Notification received from the OS when the mouse enters the game window.

Implemented on desktop and web platforms.

NOTIFICATION_WM_MOUSE_EXIT = 1003 — Notification received from the OS when the mouse leaves the game window.

Implemented on desktop and web platforms.

NOTIFICATION_WM_FOCUS_IN = 1004 — Notification received from the OS when the game window is focused.

Implemented on all platforms.

NOTIFICATION_WM_FOCUS_OUT = 1005 — Notification received from the OS when the game window is unfocused.

Implemented on all platforms.

NOTIFICATION_WM_QUIT_REQUEST = 1006 — Notification received from the OS when a quit request is sent (e.g. closing the window with a “Close” button or Alt+F4).

Implemented on desktop platforms.

NOTIFICATION_WM_GO_BACK_REQUEST = 1007 — Notification received from the OS when a go back request is sent (e.g. pressing the “Back” button on Android).

Specific to the Android platform.

NOTIFICATION_WM_UNFOCUS_REQUEST = 1008 — Notification received from the OS when an unfocus request is sent (e.g. another OS window wants to take the focus).

No supported platforms currently send this notification.

NOTIFICATION_OS_MEMORY_WARNING = 1009 — Notification received from the OS when the application is exceeding its allocated memory.

Specific to the iOS platform.

NOTIFICATION_TRANSLATION_CHANGED = 1010 — Notification received when translations may have changed. Can be triggered by the user changing the locale. Can be used to respond to language changes, for example to change the UI strings on the fly. Useful when working with the built-in translation support, like Object.tr.

NOTIFICATION_WM_ABOUT = 1011 — Notification received from the OS when a request for “About” information is sent.

Specific to the macOS platform.

NOTIFICATION_CRASH = 1012 — Notification received from Godot’s crash handler when the engine is about to crash.

Implemented on desktop platforms if the crash handler is enabled.

NOTIFICATION_OS_IME_UPDATE = 1013 — Notification received from the OS when an update of the Input Method Engine occurs (e.g. change of IME cursor position or composition string).

Specific to the macOS platform.

NOTIFICATION_APP_RESUMED = 1014 — Notification received from the OS when the app is resumed.

Specific to the Android platform.

NOTIFICATION_APP_PAUSED = 1015 — Notification received from the OS when the app is paused.